1. Field of the Invention
The present invention relates to a process for producing a fluorine-containing elastomer, and more particularly to a process for producing a fluorine-containing elastomer having a good resistance to an amine-based additive.
2. Description of Related Art
Fluorine-containing elastomers have distinguished heat resistance, chemical resistance and compression set resistance characteristic, and thus have been so far used in many fields including automobile parts. With recent trends of higher performance and lower fuel consumption for automobile engines, a higher performance is required for the engine oil. To this effect a large amount of an amine-based additive is often added to the engine oil. Thus, the fluorine-containing elastomers to be used as materials for automobile parts in contact with the engine oil requires an amine-based additive resistance.
Vinylidene fluoride-hexafluoropropene copolymers and vinylidene fluoride-hexafluoropropene-tetrafluoroethylene terpolymers are widely used as fluorine-containing elastomers, but the vulcanization products of these fluorine-containing elastomers undergo surface hardening and deterioration by engine oils and thus are not suitable for application to parts in contact with engine oils. It seems that the vinylidene fluoride-hexafluoropropene linking sites in the polymer main chain react with the amine-based additive to cause hardening.
Several fluorine-containing elastomers with an improved resistance to the amine-based additive are known on the other hand.
Tetrafluoroethylene-perfluoro(methyl vinyl ether) copolymers show a distinguished resistance not only to the amine-based compounds, but also to various polar solvents, but have poor low-temperature characteristics, such as glass transition point (Tg) as low as about -5.degree. to about 0.degree. C. and are more expensive than the above-mentioned, widely used fluorine-containing elastomers.
Tetrafluoroethylene-propylene copolymers show a good resistance to amine-based compounds and various polar solvents, but have a TR-10 as an indicator of low-temperature characteristics of 10.degree. C. and are inferior to low-temperature characteristics compared with the above-mentioned, widely used fluorine-containing elastomers.
Vinylidene fluoride-propylene-tetrafluoroethylene terpolymers or vinylidene fluoride-.alpha.-olefin-hexafluoropropene-tetrafluoroethylene quaternary copolymers have a somewhat improved low-temperature characteristic (TR-10:-8.degree. C.), though not satisfactory, and cannot be used as molding materials for the dynamic sealing due to a poor wear resistance.
Vinylidene fluoride-tetrafluoroethylene-perfluoro(methyl vinyl ether) terpolymers have distinguished resistance to amine-based additives and low-temperature characteristic (TR-10:-30.degree. C.), but have such a problem as several times higher cost than those of the above-mentioned, widely used fluorine-containing elastomers, because of the inevitable copolymerization of about 15 to about 25% by mole of expensive perfluoro(methyl vinyl ether).